A font is a typeface style such as Arial, Times New Roman, or Courier. A font consists of a set of characters. For example, for a Roman font, these characters include upper and lower case characters, numbers, punctuation, and other symbols. Fonts also include text faces such as Regular, Bold, and Italic. Moreover, font text is displayed at a particular scale called a point size. In a computer, characters of a font are represented as glyphs. A glyph includes a set of points that defines straight lines and curves, which form the outline of a character.
Text is displayed on a computer monitor by converting a glyph into a bitmap raster through a process called rasterization. During the rasterization process, a glyph outline is filled to produce a bitmap raster. The bitmap raster is displayed by imprinting it onto the computer monitor's backing store, which implicitly displays the bitmap raster on the computer monitor at a high duty cycle. The process of imprinting a bitmap raster onto the computer monitor's backing store is called blitting. Depending on the computer system, a bitmap raster may be imprinted into a window's backing store, and then imprinted onto the monitor's backing store.
Some fonts include “hints,” which are used when font characters are displayed on a computer monitor. In addition to information representing the outline of a character, glyphs of a hinted font include information about scaling the character for different resolutions. In particular, hints describe a font's stems and bowls that should be snapped to pixel boundaries. Hinting is typically used when rasterizing a glyph to a purely black and white bitmap. Hinting can also be used to increase the contrast of grayscale glyph bitmaps. Hints are added to a font when the font is designed. For example, typically, font designers must determine rules for fitting each character of a font into a grid to obtain quality raster characters. The grid fitting rules (also called hints) typically apply to character stems, bowls, and serifs. Thus, the process of adding hints to a font increases the time for designing a font. As a result, many fonts do not include hints. Because many fonts are designed without hints, it can be difficult to align key parts of character glyphs to achieve relatively high contrast, when displaying fonts on a computer monitor.